DESCRIPTION: Thromboxane A2 synthase (TXAS) converts prostaglandin H2 to thromboxane A2 (TXA2) which is a potent inducer of vasoconstriction and platelet aggregation. TXA2 is believed to be a crucial factor contributing to variety of cardiovascular and pulmonary diseases such as thrombosis, atherosclerosis, myocardial infarction and primary pulmonary hypertension. TXAS is a member of the cytochrome P450 superfamily. Unlike most cytochrome P450s, TXAS catalyzes an isomerization reaction and does not need any reductas or any other external electron donor. Characterization of the enzymology of TXAS has bee limited by its low abundance in nature. The efforts in Dr. Wang's laboratory in isolating the human TXAS cDNA and developing a large scale expression system has resulted in making the biochemical tools available to study the enzymology of TXAS. The specific aims to study the active site structure and catalytic mechanism of TXAS are: (1) to characterize the active site topology and substrate access channel, (2) to identify the heme and substrate intermediate states in TXAS catalysis, and (3) to determine the functional roles of the candidate amino acid residues involved in TXAS catalysis. In addition to TXAS enzymology, the principal investigator also proposes to study the transcriptional regulation of TXAS gene. Specific aims for this portion of the proposed study are: (4) to analyze the functional roles of the cis-acting elements of TXAS promoter, (5) to develop an in vitro transcription system to elucidate the molecular mechanism of TXAS gene transcription, and (6 to examine the involvement of NF-E2, a hematopoietic-specific transcription factor, in TXAS gene regulation. The overall goals of this application are to understand the reaction mechanism of TXAS and the mechanism of the transcription regulation of TXAS gene. Results from these studies may provide useful information for rational drug design targeted against the cardiovascula and pulmonary diseases.